Vijaykumar S. Ijeri

Chemically modified electrodes based on macrocyclic compounds for determination of Vitamin C by electrocatalytic oxidation

The voltammetric behavior of Vitamin C (l-ascorbic acid) at carbon paste electrodes and electrodes modified with aza macrocycles have been studied. The use of zinc complexes, formed in situ at the electrode surface reduced the overpotential for the oxidation of ascorbic acid by about 200 mV and enhanced the peak currents. Linearity was observed over the range of 0.6–500g/cm 3 with a detection limit of 0.1g/cm 3 by differential pulse voltammetry. The modified electrode was used for the determination of Vitamin C in multivitamin–multimineral pharmaceutical preparations, fruit juices and wine samples.

Voltammetric behavior of α-tocopherol and its determination using surfactant+ethanol+water and surfactant+acetonitrile+water mixed solvent systems

Abstract Cyclic voltammograms, at the carbon paste electrode were recorded for α-tocopherol dissolved in surfactant+ethanol+water and surfactant+acetonitrile+water mixed solvent systems containing ammonia. The oxidation potential of the vitamin was found to vary with a change in the surfactant, being more positive in cationic surfactants as compared to the anionic or nonionic surfactants. Differential pulse voltammetric technique was utilized for the determination of the vitamin in the above solvent systems. The limit of detection and the linear range varied in different surfactants, the lowest being in the Triton X-100+acetonitrile+water mixtures. Simultaneous determination of α-tocopherol and ascorbic acid was carried out. Multivitamin–multimineral pharmaceutical preparations analyzed gave satisfactory results.

Coated Wire Copper(II) Ion Selective Electrode Based On 5,6,14,15-Dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene

A coated wire copper ion selective electrode based on 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14diene as a neutral carrier in a polyvinyl chloride matrix was developed. Concentrations of Cu in synthetic samples, bath samples, cupro-nickel alloy and ore were determined. The electrode has a wide linear response to the activity of Cu(II) in the range of 1 10 1 to 1 10 6 M and the influence of pH on the membrane prepared is small.

The Complexation Behaviour of Crown Ethers with Some Divalent Transition Metal and Silver Ions in a 40%(v/v) Ethanol + Water Medium

The stability constants in 40%(v/v) ethanol + water mixture were evaluated for complexes of NiII, CoII, CuII, ZnII, MnII and AgI with the macrocyclic polyethers 15-crown-5, benzo-15-crown-5, 18-crown-6 and dicyclohexano-18-crown-6 by conductometric titrations. In addition, a potentiometric study of the CuII and AgI complexes was undertaken to compare the results with those obtained by conductivity measurements. The complexation studies indicate 1:1 complex formation between the metal ion and crown ether and the log K values are in the range 1.0−3.0. The limiting molar conductivities of the metal ions and their crown ether complexes were also determined.

Complexation of Macrocyclic Compounds with Silver Ions in Surfactant Media

This paper is a report on the complexation studies of silverions with certain water soluble crown ethers viz., 15-crown-5,18-crown-6, cyclam, diaza 15-crown-5 and certain water insolublecrown ethers viz., benzo 15-crown-5, dibenzodiaza 15-crown-4,dibenzyldiaza 18-crown-6 in some nonionic surfactants viz.,polyoxyethylated alkyl phenol (TX 100), polyoxyethylene (20)sorbiton monolaurate (Tween 20), polyoxyethylene (20) sorbitonmonoleate (Tween 80) and polyoxyethylated glyco monolaurylether (Brij 35) by potentiometry. In addition, conductometry wasalso used to study the complexation of oxa crown ethers to comparethe results obtained by potentiometry, which were found to be ingood agreement with each other. The complexation studies indicate1:1 complex formation between the silver ion and macrocycle, thelogMLn+ values being in the range 1 to 9.

Stability Constants of Some Macrocyclic Complexes of Ag(I) and Cu(II) in Mixed Solvents by Potentiometry

Stability constants of complexes of Ag(I) and Cu(II) perchlorates and nitrates with some macrocyclic compounds in 90 and 75% (v/v) DMSO+water and 75% (v/v) DMF+water media have been determined by potentiometry. Silver and copper wires, and Coated Wire Ion Selective Electrodes (CWISE) were used as indicator electrodes. It was observed that complexation is stronger when the salt is present as a perchlorate than when it is as a nitrate. For both cations the stability constant values in 75% (v/v) DMF+water were somewhat higher than in 75% (v/v) DMSO. The macrocyclic effect due to cyclization of linear amine tosylates has been observed. Competitive potentiometry has been utilized to compare some of the results.